Many different types of data storage and handling systems exist and are being used to store data cartridges at known locations and to retrieve desired cartridges so that data may be written to or read from the data cartridges. Such data storage and handling systems are often referred to as "juke box" data storage systems, particulary if they can accommodate a large number of individual data cartridges.
A typical juke box data storage system may include one or more different types of cartridge receiving devices for holding the various data cartridges. For example, one type of cartridge receiving device may comprise a cartridge storage rack or "magazine" while another type of cartridge receiving device may comprise a cartridge read/write device. The cartridge storage racks or magazines serve to provide storage locations for the data cartridges and are commonly arranged so that they form one or more vertical stacks. The cartridge read/write device may be located adjacent the cartridge stack, although the cartridge read/write device may be positioned at any convenient location. The data storage system may also be provided with a cartridge access device for accessing the various data cartridges contained in the cartridge receiving devices and a positioning device for moving the cartridge access device among the cartridge receiving devices.
If a host computer system issues a request for data contained on a particular data cartridge, a control system associated with the data storage system actuates the positioning system to move the cartridge access device along the cartridge storage rack until the cartridge access device is positioned adjacent the desired data cartridge. The cartridge access device then removes the data cartridge from the cartridge storage rack and carries it to the cartridge read/write device. The cartridge access device inserts the selected data cartridge into the cartridge read/write device so that the host computer may thereafter read data from or write data to the data cartridge. After the read/write operation is complete, the cartridge access device may remove the data cartridge from the read/write device and return it to the appropriate location in the cartridge storage rack.
While data storage systems of the type described above work well and are currently being used, the continuing need to store ever increasing numbers of data cartridges can place significant limitations on the data storage system. For example, in data storage systems of the type described above, the data cartridges may be stored in one or more vertical columns stacks which define a single cartridge access plane. While the data storage capacity of such a system may be increased by increasing the number of data cartridges stored in the vertical columns, there is a limit to the maximum number of data cartridges that can be stored in a given column. That is, the higher the column (i.e., the more data cartridges that are stored in the column), the longer it takes the data access device to access a given data cartridge, particularly if the cartridge is located at one of the extreme ends of the column. While more columns of shorter heights may be provided, this comes at the expense and difficulty of providing a positioning system capable of moving the cartridge access device vertically along a given column or stack as well as horizontally along the various rows of storage columns.
Partly in an effort to avoid the foregoing problems, data storage systems have been developed that store the data cartridges in two separate stacks or columns that define two separate cartridge access planes. For example, the data cartridges may be arranged in a pair of columns positioned on opposite sides of the cartridge access device. If this arrangement is used, it is necessary to provide the cartridge access device with a "pass-through" cartridge engaging assembly or picker that is capable of accessing the data cartridges stored in both stacks. Alternatively, such systems have been provided with "flipping" or rotating picker systems to access the data cartridges stored in both stacks.
While the "multi-plane" data storage systems of the type described above are currently being used, the pass-through, flipping, or rotating picker assemblies are relatively complex and expensive to manufacture. Such picker assemblies also tend to suffer from decreased reliability, primarily as a result of the relatively complex mechanical structure associated with such picker assemblies.
Another type of data storage system achieves the increased storage capacity associated with "multi-plane" data storage systems described above by arranging the data cartridges on a rotating magazine stack. While the rotating magazine stack usually does away with the need to provide a pass-through, flipping, or rotating picker, the mechanical complexity of the data storage system is usually just transferred from the picker to the rotating magazine stack. Consequently, data storage systems utilizing rotating magazine stacks often do not provide any significant advantages over "multi-plane" data storage systems that utilize pass-through, flipping, or rotating pickers.
Another problem associated with data storage systems of the type described above relates to the positioning system used to move the cartridge access device along the array of data cartridges. One type of positioning system, often referred to as a "lead-screw" system, mounts the cartridge access device on a lead-screw, which when turned, moves the cartridge access device up and down the array of cartridges. Unfortunately, the cantilever mounting arrangement that is often used to mount the cartridge access device on the lead-screw allows excessive transverse or rotational movement of the cartridge access device which tends to reduce positional accuracy and may make it difficult for the cartridge access device to engage the desired data cartridge.
One way to increase the stability of the cartridge access device, thus positional accuracy, of such a lead-screw positioning system is to use rigid guide rails to provide additional support to the cartridge access device. Disadvantageously, the guide rails usually comprise precision machined components which adds to the overall cost of the data storage system. Further, such guide rail assemblies are often difficult to align, and may become mis-aligned during subsequent shipping or movement of the data storage system, thereby requiring the positioning system to be re-aligned and re-calibrated before the data storage device can be placed in operation.
Consequently, a need remains for a data storage device having increased storage capacity but without the need for a pass-through, flipping, or rotating picker to access the data cartridges and without the need to resort to a moving or rotating cartridge magazine stack. Ideally, such a data storage system would provide for increased positional accuracy to reduce errors due to misalignment of the cartridge access device but without the need for precision machined guide rails. Still other advantages could be realized if the data storage system reduced the time required for initial alignment and calibration and provided increased immunity to subsequent mis-alignment, such as may occur during shipping or from rough handling.